In order to reduce the data rates in video data, such video data are compressed using an intra-frame coding method. A data rate reduction is mainly achieved by decoding only the differences between an image and a preceding image. This procedure results in the image being able to be decoded only if the preceding image has previously been decoded. Intra frames are introduced into a video stream in time intervals, these intra frames not referring to any predecessor and therefore being able to be decoded independently.
Video streams or data streams are usually transmitted within networks as packets, each packet containing a number of encoded data bytes. Each packet has a sequence number, so that a receiver may check the data stream for consistency. The streaming and decoding of an encoded data stream in the forward direction is a straightforward procedure. A decoder must wait for the arrival of a first intra frame in order to be able to decode all subsequent images from this point in time on.
Specifications or embodiments using this method include, for example, MPEG 2, MPEG 4 and the “Realtime Streaming Protocol.” These are defined by IETF, the Internet Engineering Task Force, an international organization of network specialists, in “RFC 3550,” a transmission protocol for real-time applications. An encoded video or encoded video data may be stored on a memory medium and replayed at a later point in time. The streaming of stored media data or video data in the forward direction to a remote customer is a straightforward method. However, the streaming, i.e., transmitting, of packets in a reverse, backward sequence is more complicated.
U.S. Pat. No. 5,892,882 discusses a motion picture encoding system for a memory medium which processes digital motion pictures. Furthermore, that document relates to a method for decoding and reproducing motion pictures for a special reproduction mode such as reverse reproduction. This encoding system requires little memory space and performs both decoding and reproduction at a low speed.
International Patent Document WO 01/37572 A1 discusses a method for decoding video data streams encoded according to the MPEG format which are received in a forward reproduction sequence. Decoded images which are to be replayed in a reverse sequence are produced from these video data streams. For this purpose, a limited number of decoded frames is stored for a time period, the same encoded image data being retrieved in a forward-directed reproduction to produce decoded image data using the stored frames.
U.S. Pat. No. 6,445,738 discusses a system and a method for generating trick reproduction video data streams from a compressed normal reproduction video data stream. In this case, interceded video data streams are recoded into intracoded video data streams.